1. Field of the Invention
The present invention generally relates to iontophoretic drug delivery devices, and more particularly relates to electronic circuits for use in iontophoretic drug delivery devices which deliver a controlled voltage or current to a patient receiving medication transdermally.
2. Description of the Prior Art
Iontophoresis may be defined as the electrically driven application of drugs or medications, in their ionic form, to the surface tissues of a patient. The application of electric current causes the migration of ions into the tissue, where such migration is proportional to the quantity of current applied through the iontophoretic system.
A basis iontophoretic device includes a controller and a drug delivery device, commonly called a transdermal patch. The controller may include a power source and a circuit to control the application of voltage or current from the power source to the patch. The patch generally includes two or more electrodes, the ionic medication and an electrolyte. When the patch is placed against the skin of the patient and a voltage is impressed across the electrodes, a circuit through the patient""s skin is created and current flows through the skin of the patient, driving the ionic medication into the skin and tissue to be absorbed by the patient""s body.
In some applications, it may be desirable to increase the voltage provided to the patch electrodes from the power source. This is especially true when the iontophoretic device is battery powered, and it may be necessary to increase a relatively low battery voltage to a higher, but safe, electrode voltage to more effectively drive the ionic medication into the skin and tissue of the patient. In such applications, a boost circuit or step-up DC-DC converter may be suitable for use, such as shown in FIG. 4, of U.S. Pat. No. 5,306,235.
It is an object of the present invention to provide an improved circuit design for an iontophoretic drug delivery device.
It is another object of the present invention to provide a high efficiency DC-DC converter circuit for use in an iontophoresis system.
It is a further object of the present invention to provide a self-regulating DC-DC converter circuit for an iontophoresis system which adjusts to changes in the impedance of the tissue of a patient undergoing iontophoresis.
It is yet a further object of the present invention to provide a DC-DC converter circuit which adjusts its output voltage in response to a desired drug delivery current or to variations in the impedance of a patient undergoing iontophoresis.
It is yet another object of the present invention to provide a DC-DC converter circuit which is at least partially failsafe to prevent undesired current flow to a patient undergoing iontophoresis.
In accordance with one form of the present invention, an iontophoresis system includes an iontophoretic drug delivery device, commonly called a patch, for placement against the skin of a patient, and a controller electrically connected to the patch and having circuitry for controlling current and voltage provided to the patch. More specifically, the patch includes at least a first electrode, which may act as an anode, and at least a second electrode, which may act as a cathode. The patch also includes containers or other structure for holding an electrolyte and a medication. The electrolyte and medication are situated on the patch such that they are in electrical communication with one or the other of the first and second electrodes.
The controller of the iontophoresis system includes a DC-DC converter circuit. The DC-DC converter circuit generates an output voltage which is provided to at least one of the first and second electrodes.
The controller also includes an adjustable current regulator circuit. The current regulator circuit is coupled to the other electrode and is adjustable to provide a desired current flow through the first and second electrodes and the skin of the patient when the patch is placed on the patient""s skin.
The DC-DC converter circuit is responsive to the voltage drop across the first and second electrodes. The circuit adjusts its output voltage in response to this voltage drop to provide just the voltage needed across the electrodes and adjustable current regulator for safe and effective drug delivery to the patient without the wasteful consumption of power. The controller circuitry, which includes both the DC-DC converter circuit and the adjustable current regulator circuit, is also particularly responsive to any sudden changes in current or voltage provided to the patch, such as if the patient""s skin impedance suddenly changed or the current regulator circuit is adjusted to provide a different drug delivery current to the patient during the iontophoretic process.
These and other objects, features and advantages of the present invention will become apparent from the following detailed description of illustrative embodiments thereof, which is to be read in connection with the accompanying drawings.